The present invention relates to a web steering air flotation device for printing equipment, particularly for guiding a web printed upon on both sides thereof, when travelling through various processing units, such as a dryer or the like.
U.S. Pat. No. 5,353,979 teaches a directing apparatus for guiding, deflecting, and/or diverting a web of material. A directing apparatus for guiding, transversely deflecting, and diverting a web of material that is guided over a number of rollers contains a block which is connected to a medium supply device for supplying a medium (i.e. air). The block has a curved surface over which the web can be led, the curved surface has a plurality of bores provided in each of separate sections forming the block. The sections extend transversely to the web, a plurality of separate sections are provided for the web of material and form a fluid bed for the web. Supply lines are provided that extend through the block and connect the separate sections to the medium supply device, whereby through the supply lines the medium can flow out of the bores and against the web from the medium supply device. Furthermore, control valves are located in the supply lines outside of the block for controlling the flow of the medium into the respective supply lines at variable velocities in variable volumes to supply a different fluid pressure to each separate section to create a pressure gradient across the webs width to deflect and divert the web from a first guided direction of travel to a second guided direction of travel depending on the pressure gradient which urges the web from the surface of the block.
U.S. Pat. No. 3,971,496 teaches a dual control adapter for a printing press, in a press having a one way clutch and a rod responsive to actuating devices for operating the clutch to control the press. There is provided a device in-between the actuating device and the rod to ensure that the press will operate only in response to a force occurring in a predetermined manner. The rod is connected to a pivotally mounted lever whose operation is first resisted and then effected by successive operation of two linkages responding to energizing of a pressure cylinder. One linkage normally provides a support function under the lever for positively preventing it from effecting movement of the rod. A pair of hand-switches are connected to a valve for energizing the cylinder when both hands of an operator are on the respective switches. With the device of the invention in place and the actuating cylinder energized, the first operation is to pull the support out of a locking position to permit downward movement of the lever. This is followed immediately by engagement of the lever by the second linkage that draws the lever downward sufficiently to affect such movement of the pull rod as to energize the clutch and initiate an operation of the press.
U.S. Pat. No. 5,152,080 teaches a steerable air apparatus. The apparatus floatingly supports a web and maintains the web in a substantially straight path as it travels through the dryer. The apparatus contains a steerable air bar assembly with one or more adjustable air bars, each having an elongated surface from which air may be discharged. The elongated surface is in an opposing relation to the running web and has two ends. Further, an air supply device in fluid communication with the air bars and an adjustment device for altering the orientation of the elongated surfaces of the adjustable air bars with respect to the running web are provided. In a preferred embodiment the orientation of the surfaces is adjusted such that each surface rotates about an axis which is substantially parallel to the longitudinal center line of the running web. The steerable air bar assembly is positioned in a web dryer such that the web is guided through the dryer in a substantially straight path. A plurality of such steerable air bar assemblies can be used in a web dryer. The dryer can also include one or more fixed air bars. Air bars can include back pressure devices for creating an opposing force to urge the web back to a substantially centered position. The back pressure device preferably has one or more edge dams preferably disposed at or near the ends of one or more fixed air bars in the web dryer.
In the technical field the need for web steering arises when webs having laterally varying tensile properties are displaced laterally while being transported through a dryer span (i.e. a static web shift). A web shift can be compensated for after traveling over the span of the dryer by commercial web guides or in the dryer span when the shift occurs. In some cases the web shift in the dryer can be too large to be corrected by the web guide.
It is accordingly an object of the invention to provide a web steering air flotation device for printing equipment that overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which variations of pressure gradients across a width of the air bars assigned to a web travel plane is performed. Still further it is an object of the present invention to provide compensation for a lateral web shift of webs having laterally varying tensile properties.
With the foregoing and other objects in view there is provided, in accordance with the invention, an air bar for steering a web of material, including an air bar body having a hollow interior formed therein, the hollow interior to be subjected to an air flow providing an air pressure formed under the web of material; at least one air jet exit is connected to the hollow interior for conducting the air flow to control a lateral travel direction of the web of material; and a metering device is associated with the hollow interior and is disposed to selectively restrict the air flow through the at least one air jet exit.
The solution according to the present invention presents numerous advantages. By correcting lateral web shifts already upon passing a dryer, further web guide compensation devices can be eliminated or simplified, since large lateral deviations of the web after passage through the dryer no longer occur. Thus, upon certain applications web guides to be disposed after the exit of the dryer no longer have to be used, since web shifts are already actively compensated for in the dryer. Preferably the air bars according to the present invention are disposed above and below the web travel plane.
According to further details of the present invention, the metering devices substantially extend along the horizontal direction. The metering devices being fully integrated into the air bars. The metering devices substantially extend perpendicular to the web of material and cover an entire width of a travelling web of material.
The metering devices, which are fully integrated into the air bars allow for a movement of the metering devices with respect to air jet exits disposed on the air bar bodies. The metering devices are mounted movably to allow for a relative movement of the metering devices relative to the air jet exits or orifices that are in fixed location on the air bars.
In an alternative embodiment, upon a rotational movement of the metering device in a first direction (i.e. clockwise) about the pivot point, a degree of coincidence between the apertures tends to increase on one side of the air bar while decreasing on the other side of the air bar, thus increasing the air flow rate on one side and decreasing the air flow rate on the other side through the air jet exits. With this difference in the air flow rates and the resulting pressure gradients, the web of material is shifted in the lateral direction (perpendicular to the travel direction). On the other hand, upon a rotational movement of the metering devices in a second direction (i.e. counter clockwise) about the pivot point, the degree of coincidence between the apertures tend to decrease the air flow rate on one side and increase the air flow rate on the other side of the air exit jets thus shifting the web of material in a lateral direction opposite to that of the first rotational movement.
In the present invention there is disclosed a still further embodiment in which the metering device moves about a pivot axis, to vary slots formed between the edges of the metering device itself and adjacent walls of an air bar body that feed the air jet exits. With respect to the movements of the metering device, adjustment elements are provided to vary the shape of the slots formed between the metering device and the walls of the air bar body. In this manner, the air flow rate is controlled through the air jet exits as a whole and also in regards to each side of the air jet exits for causing a lateral shift in the web of material.
In a still further embodiment, on top of the air bars, spacing bodies are disposed across the width of the web of material for spacing the air jet exits from one another. Air exchange openings (apertures) and control ports are disposed on the metering device allowing for variations of the cushion pressure formed below the web of material travelling in a web travel plane. For adjustment purposes, the control ports are provided for aligning with the apertures for controlling an air flow into an exhaust channel formed in the air bar. The control ports can be manually, mechanically or electrically actuated for controlling a movement of the control ports.
The air bars according to the present invention are intended to be used in air flotation devices for contactless conveying of web-like material or in dryers assigned to rotary printing presses.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a web steering air flotation device for printing equipment, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.